A spark plug for use in a combustion apparatus, such as an internal combustion engine or the like, includes, for example, a center electrode extending in an axial direction, an insulating body provided around an outer circumference of the center electrode, a cylindrical metal shell attached to an outer circumference of the insulating body, and a ground electrode having a proximal end portion joined to a distal end portion of the metal shell. The ground electrode is arranged, with its roughly middle portion being bent, such that a distal end portion of the ground electrode opposes the distal end portion of the center electrode, whereby a spark discharge gap is formed between the distal end portion of the center electrode and the distal end portion of the ground electrode. In addition, recently, there has been proposed a technique for enhancing wear resistance by joining a noble metal tip to the spark discharge gap forming portion of the distal end portion of the center electrode or the distal end portion of the ground electrode. In this instance, the noble metal alloy constituting the noble metal tip is expensive, and thus, in order to suppress an increase in manufacturing cost, the use of a relatively thin noble metal tip is considered.
When the noble metal tip and the center electrode are joined to each other, laser welding using a YAG laser is generally used (for example, refer to Patent Document 1). That is, the laser beam is intermittently irradiated onto the outer circumference of the border portion between the noble metal tip and the center electrode, so that a molten portion is formed by fusing each component to join the noble metal tip and the center electrode together.